1. Field of the Invention
The present invention relates to fast and efficient data downloading in wireless communications.
2. Description of Related Art
There exists a technique for downloading a large amount of data from a server (access point) to a client (mobile device) at a high speed by using millimeter wave (mmWave) wireless communication and conventional wireless communication (WiFi, Bluetooth, 3G, etc.).
An example of a common application of this technique in daily life is the file downloading services provided at a Kiosk. This is an on-demand data transfer service in railway stations in Japan such that a mobile user can instantly download multimedia, such as video and books, during the user's travel.
A communication line using mmWave is characterized by fast data transmission capabilities, but low robustness when compared with conventional wireless communication. On the other hand, conventional wireless communication is characterized by high robustness, but a relatively low data transmission rate (communication speed) when compared with mmWave.
The above characteristics are summarized in the table below.
Out-of-bandIn-bandconventional wireless link mmWave(WiFi, 3G, Bluetooth, etc.)Data transmission ratehighlowRobustnesslowhigh
An ideal situation is if the two types of wireless communication with different characteristics can be complimentarily used to realize fast and efficient file transfer. That is, to make use of the high speed of mmWave, highly robust control is necessary. Control here includes connection and disconnection of the link, and detection and retransmission of lost packets. For efficient transfer, the packet loss must be quickly detected and the lost packets must immediately be retransmitted.
Japanese Patent No. 3351653 discloses a technique of retransmitting a packet by using both a high-speed line and a low-speed line. The technique addresses data retransmission for a data error determined by an error check, but no description is given for the case of packet loss.
Another known technique is packet loss detection based on timeout, as used in protocols such as the TCP/IP protocol. Unfortunately, application of this technique to a Kiosk download service would not be efficient due to the need to wait until timeout.